Exhaust aftertreatment device, including chemical mixing and acoustic effects

ABSTRACT

An exhaust aftertreatment device ( 10 ) includes an aftertreatment element ( 24 ) for treating internal combustion engine exhaust, an injector ( 26 ) for injecting chemical species mixing with the exhaust prior to reaching the aftertreatment element, and a turbulator ( 36 ) turbulating the exhaust to enhance the noted mixing. In a desired combination, a two-stage integrated perforated tube combination structure includes a turbulent mixing tube ( 38 ) disposed in an acoustic tube ( 40 ) and concentrically surrounded thereby.

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application is a Continuation-In-Part of U.S. patentapplication Ser. No. 09/981,171, filed Oct. 17, 2001, incorporatedherein by reference.

BACKGROUND AND SUMMARY OF THE INVENTION

[0002] The invention relates to aftertreatment devices for internalcombustion engine exhaust, and more particularly to combined chemicalmixing and acoustic effects.

[0003] To address engine emission concerns, new standards continue to beproposed for substantial reduction of various emissions, includingNO_(X) and particulate emissions. Increasingly stringent standards willrequire installation of aftertreatment devices in engine exhaustsystems. Some of the aftertreatment technologies require certainchemical species to be injected into the exhaust system. For example, HCor fuel is injected in some active lean NO_(X) systems, and additivessuch as cerium and iron are injected for diesel particulate filterregeneration, and urea solution is injected in selective catalyticreduction (SCR) systems for NO_(X) reduction. These injected chemicalspecies need to be well mixed with exhaust gas before reaching catalystsor filters for the systems to perform properly.

[0004] Perforated tubes are widely used in engine exhaust systems fornoise reduction. If designed properly, perforated tubes can also createhigh intensity turbulent flow. The turbulent flow will promote turbulentdiffusion of the chemical species and therefor enhance the mixingprocess.

[0005] In one aspect of the present invention, improved chemical mixingis provided.

[0006] In another aspect, the invention integrates a turbulent mixingtube with an acoustic tube into an engine exhaust system.

[0007] In another aspect, the invention provides an engine exhaustsystem with two-stage perforated tubes. The system is designed not onlyto reduce the noise level, but also to enhance the mixing processes ofchemical species which are injected into the exhaust system, includingfor regeneration of diesel particulate filters and for controllingengine NO_(X) emissions.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008]FIG. 1 is a side schematic sectional view of an exhaustaftertreatment device in accordance with the invention.

[0009]FIG. 2 is like a portion of FIG. 1 and shows another embodiment.

[0010]FIG. 3 is like a portion of FIG. 1 and shows another embodiment.

DETAILED DESCRIPTION OF THE INVENTION

[0011]FIG. 1 shows an exhaust aftertreatment device 10 including ahousing 12 extending axially along an axis 14, and having an upstreaminlet 16 for receiving engine exhaust as shown at arrow 18, and having adownstream outlet 20 for discharging the exhaust as shown at arrow 22.An aftertreatment element 24, for example an SCR catalyst and/or anoxidation catalyst and/or a particulate filter, is provided in thehousing for treating the exhaust. An injector 26 is provided in thehousing for injecting chemical species as shown at 28 mixing with theexhaust prior to reaching aftertreatment element 24. For example, in oneembodiment, aqueous urea solution is injected from reservoir or tank 30through tubular conduit 32 and is injected at nozzle or tip 34, thoughother chemical species may be used.

[0012] A turbulator 36 is provided in the housing upstream ofaftertreatment element 24 and turbulating the exhaust to enhance thenoted chemical mixing upstream of aftertreatrnent element 24. Theturbulator is provided by a perforated mixing tube 38. Also provided inthe housing is a perforated acoustic tube 40 quieting the exhaust.

[0013] It has been found that improved performance results fromproviding the tubes 36 and 40 with different perforation hole sizes,namely by providing the mixing tube 36 with larger perforation holesizes than acoustic tube 40. In a particular situation, it has beenfound that improved performance results when mixing tube 36 has aperforation hole size greater than or equal to one-quarter inch, andwhen acoustic tube 40 has a perforation hole size less than one-quarterinch, preferably less than or equal to one-eighth inch. It has beenfound that the noted perforation hole size greater than or equal toone-quarter inch for mixing tube 36 creates improved turbulent diffusionand mixing of the injected chemical species, and that the notedperforation hole size less than one-quarter inch for acoustic tube 40minimizes aeroacoustic effects. In preferred form, perforation holes 48of turbulator 36 are square shaped as shown at 47 for generatinghomogenous and isotropic turbulence, though circular holes are alsoacceptable as optionally shown at 49. Perforation holes 52 and 54 ofacoustic tube are preferably circular.

[0014] In the preferred embodiment, mixing tube 36 is conical,preferably frustoconical with a closed nonperforated downstream end 42.Further in the preferred embodiment, acoustic tube 40 is cylindrical,with a closed nonperforated downstream end 44. Conical mixing tube 38has a tapered sidewall 46 with uniform porosity as shown at perforations48. Cylindrical acoustic tube 40 has a sidewall 50 with varied porosity,for example as shown at upstream perforations 52 having a higher densitythan downstream perforations 54. The varied porosity along a cylindricalsidewall has been found to provide a more even flow therealong. Porositymay also be varied by varying the size, distance, and number ofperforation holes. Mixing tube 38 is disposed in acoustic tube 40 andconcentrically surrounded thereby. Each of tubes 38 and 40 is upstreamof aftertreatment element 24. In preferred form, mixing tube 38 isupstream of acoustic tube 40, and mixing tube 38 is within acoustic tube40.

[0015] Mixing tube 38 has an upstream end 56 and a downstream end 58,and the noted perforated sidewall 46 extending therebetween. Sidewall 46is perforated at perforations 48 with a porosity selected to providesubstantially uniform resistance and even flow along mixing tube 38. Inpreferred form, the noted substantially uniform resistance and even flowis provided in combination by a conically tapered sidewall 46 perforatedwith uniform porosity. The conical shape points downstream such thatmixing tube 38 narrows to smaller cross-sectional areas as mixing tube36 extends from upstream end 56 to downstream end 58. As above noted,the conical shape is truncated at 42 at downstream end 58.

[0016]FIG. 2 uses like reference numerals from above where appropriateto facilitate understanding. In FIG. 2, a screen 60 extends frominjector 26 at nozzle or tip 34 and is disposed in mixing tube 38.Injector 26 at nozzle 34 injects the chemical species along a spraypattern as shown at 28, FIG. 1, having an injection boundary 62. Screen60, FIG. 2, extends from the injector along injection boundary 62. Asabove noted, mixing tube 38 has a conical shape pointing downstream.Screen 60 has a conical shape pointing upstream, namely to an apex ortruncated apex at injector tip or nozzle 34. Conical mixing tube 38 atits tapered sidewall 46 convergingly tapers as it extends downstream.Screen 62 divergingly tapers as it extends downstream.

[0017]FIG. 3 uses like reference numerals from above where appropriateto facilitate understanding. In FIG. 3, conical screen 60 of FIG. 2 isreplaced by a spherical screen 64 around injector tip 34 and extendingtherefrom.

[0018] As is known, the injected chemical species undergoes chemicalprocesses in mixing with the exhaust, including chemical decomposition,chemical reaction, and phase change. In a further embodiment, injector26 is heated by a heat source in addition to heating by the exhaust. Inone embodiment, the heat source is provided by a voltage source 70external of the housing and a pair of electrical conductors 72, 74connecting the voltage source to the injector. Heater 70 is provided forheating the injector and accelerating the noted chemical processes.

[0019] Also as known, the injected chemical species is subject tocoagulation and coalescence. In a further embodiment, a screen such as60 or 64 is provided, extending from the injector, and a heater isprovided for heating the screen to minimize the noted coagulation andcoalescence. In one embodiment, such heat source is provided by the samevoltage source 70 noted above, and a pair of electrical conductors 76,78 connecting the voltage source to screen 60 or 64.

[0020] It is recognized that various equivalents, alternatives, andmodifications are possible within the scope of the appended claims.

What is claimed is:
 1. An exhaust aftertreatment device comprising: ahousing extending along an axis and having an upstream inlet forreceiving said exhaust, and a downstream outlet for discharging saidexhaust; an aftertreatment element in said housing for treating saidexhaust; an injector in said housing upstream of said aftertreatmentelement and injecting chemical species mixing with said exhaust prior toreaching said aftertreatment element; a turbulator in said housingupstream of said aftertreatment element and turbulating said exhaust toenhance said mixing upstream of said aftertreatment element.
 2. Theexhaust aftertreatment device according to claim 1 wherein saidturbulator comprises a perforated mixing tube.
 3. The exhaustaftertreatment device according to claim 2 wherein said perforatedmixing tube has a perforation hole size greater than or equal toone-quarter inch.
 4. The exhaust aftertreatment device according toclaim 2 wherein said perforated mixing tube has square perforationholes.
 5. The exhaust aftertreatment device according to claim 2 whereinsaid mixing tube has an upstream end and a downstream end, and aperforated sidewall extending from said upstream end to said downstreamend.
 6. The exhaust aftertreatment device according to claim 5 whereinsaid sidewall is perforated with a porosity selected to providesubstantially uniform resistance and even flow along said mixing tube.7. The exhaust aftertreatment device according to claim 6 wherein saidsubstantially uniform resistance and even flow is provided incombination by a conically tapered said sidewall perforated with uniformporosity.
 8. The exhaust aftertreatment device according to claim 5wherein said mixing tube is conically shaped.
 9. The exhaustaftertreatment device according to claim 8 wherein said conical shapepoints downstream such that said mixing tube narrows to smallercross-sectional areas as said mixing tube extends from said upstream endto said downstream end.
 10. The exhaust aftertreatment device accordingto claim 9 wherein said sidewall is perforated with uniform porosity.11. The exhaust aftertreatment device according to claim 9 wherein saidconical shape is truncated at said downstream end.
 12. The exhaustaftertreatment device according to claim 1 wherein said turbulatorcomprises a mixing tube, and comprising a screen extending from saidinjector and disposed in said mixing tube.
 13. The exhaustaftertreatment device according to claim 1 wherein said injector injectssaid chemical species along a spray pattern having an injectionboundary, and comprising a screen extending from said injector alongsaid injection boundary.
 14. The exhaust aftertreatrnent deviceaccording to claim 13 wherein said turbulator comprises a mixing tubehaving a conical shape pointing downstream, and said screen has aconical shape pointing upstream.
 15. The exhaust aftertreatment deviceaccording to claim 14 wherein said mixing tube convergingly tapers as itextends downstream, and said screen divergingly tapers as it extendsdownstream.
 16. The exhaust aftertreatment device according to claim 1comprising a spherical screen around said injector and extendingtherefrom.
 17. The exhaust aftertreatment device according to claim 1wherein said injected chemical species undergoes chemical processes inmixing with said exhaust, including chemical decomposition, chemicalreaction, and phase change, and comprising a heater heating saidinjector and accelerating said processes.
 18. The exhaust aftertreatmentdevice according to claim 1 wherein said injected chemical species issubject to coagulation and coalescence, and comprising a screenextending from said injector, and a heater heating said screen tominimize said coagulation and coalescence.
 19. The exhaustaftertreatment device according to claim 1 wherein said injector isupstream of said turbulator.
 20. The exhaust aftertreatment deviceaccording to claim 1 wherein said aftertreatment element is a catalystelement.
 21. The exhaust aftertreatment device according to claim 1wherein said aftertreatment element is a filter element.
 22. An exhaustdevice comprising: a housing extending along an axis and having anupstream inlet for receiving said exhaust, and a downstream outlet fordischarging said exhaust; an injector in said housing for injectingchemical species mixing with said exhaust; a turbulent mixing tube insaid housing turbulating said exhaust and enhancing said mixing; anacoustic tube in said housing quieting said exhaust.
 23. The exhaustdevice according to claim 22 wherein each of said tubes is perforated.24. The exhaust device according to claim 23 wherein one of said tubeshas a different perforation hole size than the other of said tubes. 25.The exhaust device according to claim 24 wherein said mixing tube has alarger perforation hole size than said acoustic tube.
 26. The exhaustdevice according to claim 25 wherein said mixing tube has a perforationhole size greater than or equal to one-quarter inch to create turbulentdiffusion and mixing of said injected chemical species, and wherein saidacoustic tube has a perforation hole size less than one-quarter inch tominimize aeroacoustic effects.
 27. The exhaust device according to claim23 wherein said turbulent mixing tube is perforated with squareperforation holes and in combination said acoustic tube is perforatedwith circular perforation holes.
 28. The exhaust device according toclaim 23 wherein said mixing tube is conical and in combination saidacoustic tube is cylindrical.
 29. The exhaust device according to claim28 wherein said conical mixing tube has a tapered sidewall with uniformporosity and in combination said cylindrical acoustic tube has asidewall with varied porosity.
 30. The exhaust device according to claim29 wherein said mixing tube is disposed in said acoustic tube andconcentrically surrounded thereby.
 31. The exhaust device according toclaim 23 comprising an aftertreatment element in said housing fortreating said exhaust, and wherein each of said tubes is upstream ofsaid aftertreatment element.
 32. The exhaust device according to claim31 wherein said mixing tube is upstream of said acoustic tube.
 33. Theexhaust device according to claim 32 wherein said mixing tube is withinsaid exhaust tube.